Regioselective and stereoselective benzylidene installation and one-pot protection of D-mannose.

Oligosaccharide syntheses are an important source of well-defined sugar constructs particularly needed for the evaluation of structure–activity relationships. The chemical assembly of oligosaccharides requires several building blocks, that is, glycosyl donors and acceptors, which are prepared in multistep processes and in a generally tedious and time-consuming manner. Having developed one-pot procedures meant to minimise the effort in sugar building block preparation, we tackled herein the one-pot preparation of fully protected and 2-, 3-, 4-, and 6-alcohol derivatives of D-mannose, a widely distributed monosaccharide. As a consequence of the hydroxyl group pattern of D-mannose, regioselective and stereoselective benzylidenations were developed and later seamlessly utilised as the first transformation in the one-pot procedure.